Compound master cylinder



A. E. ROY

COMPOUND MASTER CYLINDER March 30, 1948.

Filed March 17, 1942 Patented Mar. 3(4), 1948 4ssen UNITED STATES PATENT QFFICE 3 Claims.

This invention relates to a hydraulic brake mechanism, and which is particularly adapted for use in connection with hydraulic mechanisms.

An object of my invention is to provide a novel hydraulic brake mechanism for hydraulic braking systems, whereby the initial movement of an operating lever causes sufficient pressure to be transmitted to the pressure cylinders of the braking system to actuate a brake shoe into initial contact with the braking surface of a brake drum, while further movement of the operating lever causes a high pressure to be applied to the brake cylinders for braking purposes.

Anoth'er object of my invention is to provide a novel hydraulic brake mechanism, including alow-pressure cylinder and a high-pressure cylinder, coaxially arranged, and having novel piston elements mounted on a common hub, and a single inlet for the fluid, serving both cylinders.

Another object of my invention is to provide a novel hydraulic brake mechanism, comprising a low-pressure cylinder and a high-pressure cylinder, which are in communication with' one another durng the initial operation of the mechanism, and including novel valve means to cut oii communication between the highand low-pressure cylinders when the piston member has moved forward on its operating stroke, and to prevent the pressure in the low-pressure cylinder from rising above a pre-determined value.

Still another object of my invention is to provide a novel hydraulic brake mechanism, including highand low-pressure cylinders, and a novel valve-and-port means, whereby Vwhen starting the operative movement of the pistons in the cylinders, the pressure in the low-pressure cylinder, during the initial movement of the pistons, is quickly transferred to the high-pressure cylinder for the purpose of taking up slack in th'e brakemechanism ports, `and then pressure is transmitted at a higher value in the high-pressure cylinder by further operative movement of the pistons, and thereafter any subsequent pressure in the low-pressure cylinder is relieved during further operation ofthe mechanism.

A still further object of my invention is to provide a novel hydraulic brake mechanism, wherein the fluid pressure is controlled by a novel valveand bypass means to obtain proper balance of the fluid pressure during the compression stroke.

A feature of my invention resides in the absence of cutting on the piston cups, due to the fluid moving under high velocity, and also the rapid movement of the Valve mechanism during the initial forward movement of th'e pistons.

Other objects, advantages and features of invention may appear from the accompanying drawing, the subjoined detailed description, and the appended claims.

In the drawing:

Figure 1 is a vertical sectional View of my hydraulic brake mechanism, and showing the piston in retracted position.

Figure 2 is a sectional View taken on line 2-2 of Figure 1. l

Figure 3 is a bottom-plan View of the valve cage, and with the flat valve removed.

Figure 4 is an enlarged view of the connections between the pistons.

Referring more particularly to the drawing, my hydraulic brake mechanism includes a low-pressure cylinder I and a high-pressure cylinder 2, the high-pressure cylinder being smaller in diameter than the cylinder I and arranged coaxially therewith. The pressure release-and-control means is generally indicated at 3. This control-and-release means is for the low-pressure cylinder and is arranged in a iiuid reservoir, and also serves to provi-de communication between the reservoir and the cylinder I. A brake or operating pedal is pivoted at 5 to an arm 6, this extending from the housing of the brake mechanism.

The brake pedal i also includes a lower arm 1,

pivotly connected by a bolt 8 to one end of a push' rod S. This push rod is rounded at its inner end and engages or enters the recess Ill, formed in the back of the hub I I, for th'e purpose of forcing the hub inwardly into the cylinders I and 2, upon depression of the brake pedal 4.

An oil or fluid reservoir l2 is provided with an air bleed I3, which serves to keep the reservoir in communication with the atmosphere. The hub I I is provided with a low-pressure piston head I4 at one end, and a high-pressure piston head I5 at the other end. A cup of leather, rubber, or the like I5 is Iprovided on the low-pressure piston i4; and, similarly, a cup ll is provided on the high-pressure piston l5. A spring l'is positioned within the cylinder I and between the inner face of the piston lhead Ill, and an abutment IS, which forms the inner end of the cylinder 2. This spring serves to return the piston assemblies to retracted or inoperative position, as shown in Figure 1. The piston assembly is retained against displacement from the open end of the cylinder I by a retaining ring 2li., which is seated in a suitable groove and is preferably of the snap type. The 'highpressure piston I5, formed on the inner end of the hub II, is provided with a central port 2l. A valve head 22 on the front end of the hub II seats in the port 2| to close this port on a. forward movement of the hub relative to the piston I5. A plurality of ducts 23 extends through the forward end of the hub I I and communicates with the back of the piston I 5, permitting uid to pass through the port 2|, and thence into the highpressure cylinder 2, as will be subsequently described. The piston I has a limited sliding movement on the hub II, by means of aspring ring 24, slidably mounted in a slot 25 in the forward end of the hub II. One end of the ring 24 is bent Y outwardly to seat in a hole or slot in the bore4 of nism. A boot or cover 28 enclosesthe `open end of,l the cylinder I for the purpose of excluding dust. The relief valve assembly B'Vinclude's a cage 29, which screws into 'the upper wall of the reservoir I2, and is seated in the lower wall ci the i reservoir. A fiat valve 3e is mounted iin. the cage 29, and gravity normally holds this valveV iin vropen position. This valve controls a plurality Aof bypass ports 5I, and closes these port'swhen the valve i's'forced upwardly by pressure Yin the cylinthe hub I I and the attached pistons to the initial position, and also returns the pedal to retracted position. The valve 30 will now drop open and uid from the reservoir I2 will pass through the ports 3| to reiill the cylinder I.

Having described my invention, I claim:

l. In hydraulic brake mechanism the combination with a two-stage master cylinder having high and low Vpressure cylinders,V ofa reservoir connected to said low pressure cylinder by valving mechanism which includes: a valve Cage having a plurality of .ports connecting said reservoir and said low pressure cylinder, one of said ports being .modified to orm a bleed port; a flatV gravity operated valve, vertically movable in said cage and adaptedv to close all of said ports except said bleedV when pressure increases in said cylinder; and a spring operated valve connecting said cylinder and reservoir and adapted to open when said pressure increases and to close when said pressure decreases suiiiciently to open said nat valve.'

2. In hydraulic brake mechanism the combination with a two-'stage master cylinder having high and low pressure cylinders, of a reservoir connected to 'said low pressure cylinder by'valving mechanism which includes: a valve cage having a der I. A small bleed port 32 is always open even .l

'when the valve 30 is closed to permit .fluid to pass Y inte the reservoir when the main check valve .is

closed. VTheY main check valve consists oi" a ball Y 33, which is lpressed lon to its seat bya :spring 34. The `ball33 is seated in the relief port 3 5,

throughV which huid is forced, as thepiston =if4 moves `forwardly. rThe at valve 30 is very light, fand, therefore, will quickly close soo'n as "the piston I4 starts to move forwardly; Zl'iilrler plug 3'6 is provided in the cage 2li for the purpose of repfl'enisliing the supply of fluid. i

v'The operation of my device -is as lfollo'ws: Assuming the parts are initially 'inthe released or retracted position, 'as shown in Figure A1, whenthe Apedal Msdepressed the piston assembly, 'including the hub Il I, starts the compression stroke, and

"nui'd 'in the low-pressure cylinder 1 is displaced.

The valve 3U 'closes at once and the piston I5 Tis pushed forwardly-opening the 'port :21, andthe oil iiows through the ducts 23 and 'thence Vthrough the Vport 2l into the cylinder'2. This initial move- Y ment 'serves to immediately ll the ldelivery pipes, such 'as 21, as well as the brake cylinders'dueto the large 'areafof the piston 14 and the cylinder I. This `causes the brake shoes to engage the brake jdruinwith .a minimum movement o'ffthe pedal I. The pressure in the cylinder-.2, thereafter `becomes high enough zto momentarily check 'forward :moveinent ofthe piston I5 and allow the valve headto close the part 21, after which'excess fluid-fromme :low-pressure cylinder il raises the ball 33, "and 'enters'th'ereservoir I2 `through the port 35. :The high-pressure cylinder f2 is :new :sealed against Y escape of fluid through any xpath, except through the'outiet pipe =2 l, V'and continued :depression 'ofthe pedal lapplies the :full pressure of iluidV in the Y Number port connecting said Vreservoir and saidlow pressure cylinder, said port being modified to 'form a bleed port; a .normally open valve verticallyV movable in said cage and adapted to close said iir'st port but not said bleed port when pressure increases iin said cylinder; and rva normally .closed relief valve connectingfsaid cylinder and reservoir and adapted to open when said pressure `further increases. Y

3. In hydraulic brake mechanism the combination with a two-stage master cylinder having high Yand low' pressure cylinders, `of a reservoir connected to said low pressure cylinder by valving mechanism which includes: a valve cage having a port connecting said reservoir and said low pressure cylinder; said port being modied to'form va bleed port; Aa gravity operatedrvalve vertically movable in said cage and adapted to close said Airst port but not said bleed when pressure increases 'in said cylinder; and a spring operated valve connecting said cylinder and reservoir and 'adapted to open when Ysaid pressure further increases. Y

ALBERT E. ROY.

` REFERENCES Vorigin The following references are 'of record in `the file -of this patent:A 'y Y UNITED STATES PATENTS Name [Slate Carroll July 8, 1930 'Sinclair May l5, 1934 Leuschner Nov.Y A26, 1935 La Brie Nov. '9, "1937 2,190,238 Lepersonne Feb. I3, 1940 Loweke Sept-1'?, 1940 'Weihe1 Oct. 8, 194'() VBowen Feb. l0, 1942 FOREIGN PATENTS Country Y Number Date Bau-ghn Dec. 7,1937 Y Carroll Mar. 15,1938V 'Lambert July 18, 1939 K France Feb. 1,V 1937 

